There has been known a programmable logic controller (PLC) used as a control device for a manufacturing machine in an automated factory and the like. For example, the programmable logic controller is administered using a computer (e.g., a commercially available personal computer) having installed therein software called a tool, or a display unit used for setting the programmable logic controller.
Some networks for connecting the programmable logic controller, the computer and the display unit utilize the Ethernet (registered trademark). When one programmable logic controller and one computer are connected to each other on such a network, communication can be established between the programmable logic controller and the computer even if the respective IP addresses are unknown, as disclosed in the third paragraph of Japanese Unexamined Patent Publication No. 2009-267720 (Patent Document 1).
On the other hand, in a case where a different programmable logic controller is erroneously connected to a network where one programmable logic controller and one computer are connected to each other, the erroneous transmission of packets can be prevented by storing the identification information of the originally connected programmable logic controller, as disclosed in Japanese Unexamined Patent Publication No. 2009-267720.